AT chronic leaks

I am currently rebuilding my drive line on an automatic 1994. I want to stop my chronic AT leak, which manifests itself after 2-3 days of sitting. I understand this to be a valving problem, where the fluid is allowed to continue to drain into the reservoir under the car. Anyone have any advice/ insights/ experience with this problem? Thank you.

What makes you think it is a valving problem?

You need to find exactly where the leak is coming from. Often the pan gasket leaks, and sometimes the reservoir o-ring leaks. My '88 has a leak from the torque converter (front of the transmission). If there has been a lot of leaking you'll need to clean everything off to better see the source. If you can get under there an take a picture of the source the experts here can advise you.

Thank you for the quick response.
When I park my 928, the clear reservoir slowly fills to overflowing after a few days. Otherwise, there are no leaks visible from any other source. The transmission itself is dry, and I have replaced the reservoir just to eliminate it as a possible source. FYI: I am really careful about maintaining the correct AT fluid level, and luckily I have a lift in my garage to help accomplish this. I suspect a check valve problem, but this is just a hunch. When I drive on a regular basis, there is no leak.
Thanks again for any comments.